Delays of around 20 minutes is expected on the Southern train service to Brighton from London Bridge, as Network Rail blamed "signalling failures".
A spokesman for Network Rail said:
A signalling problem at London Bridge means platforms 9 and 10 are unavailable to trains for the remainder of the day.
This is affecting Southern services in and out of the station and passengers are advised to check with Southern or National Rail Enquiries before travelling.
We are investigating the cause of the problem and apologise to passengers for the disruption this will cause.